Railroads remain one of the most efficient means for transporting freight and passengers over relatively long distances. Yet, like many industries, the railroad industry is facing numerous challenges related to the upward trend in the cost of fossil fuels and increasing pressure to limit the impact of trains on the environment. The root cause for many of these challenges is the propulsion systems traditionally used in railroad locomotives.
Diesel-electric locomotives employ a diesel engine to drive an electric power generator, which in turn drives a set of traction motors that rotate the locomotive wheels. Diesel-electric locomotives have the advantage of requiring a minimal amount of support infrastructure and thus are particularly suited for providing transport across remote geographical regions. On the other hand, because diesel-electric locomotives consume diesel, they contribute to urban air pollution and are subject to operating costs tied directly to the cost of oil.
Catenary-electric locomotives run directly from an electricity source, typically electric lines running above the railroad tracks. Catenary-electric locomotives are cleaner-operating on a locomotive-by-locomotive basis than diesel-electric locomotives; however, catenary-electric locomotives must be viewed as small parts of a much larger distributed power system, which includes an electricity generation plant, transformers, and a system of transmission lines required to bring electricity to the locomotives as they run down the tracks. This large distributed power system is typically unsuitable for remove geographic regions and overall is less efficient than a system utilizing diesel locomotives.
Railroad locomotives come in different sizes and configurations, depending on the specific task they are required to perform. For example, line-haul freight locomotives, which are commonly seen running along the rail-lines in the U.S., are larger and more powerful systems designed to move fully assembled trains over long distances. On the other hand, switch locomotives (“switchers”) are smaller systems primarily used in rail yards for moving cars during the assembly and disassembly of trains. In any case, locomotive designs must be robust, given the day to day stresses to which locomotives are subjected.
Alternative locomotive propulsion systems, which address the problems with diesel-electric and catenary-electric propulsion systems, would be a significant benefit to the railroad industry. However, any such alternative systems must be capable of meeting the rigors experienced by locomotives everyday, including the shock loads generated during the coupling of rail cars. Additionally, propulsion systems that are applicable to different types of locomotives (e.g. line-haul freight locomotives and switchers) would be an additional and significant advantage.